There is no "market" for textbooks. Professors assign a single textbook, and students are forced to buy it. If a class could somehow allow for different textbooks would allow students to pay for cheaper textbooks and create price competition. But it's hard to do in practice if not impossible.

I didn't say they should mandate a fixed price. I said the book publishers should charge a fair price, one that decreases the amount of pirating because it's low enough so that it's not worth it for students to pirate. That's up to them. Until they do, I fully support pirating of textbooks.